This invention relates to a method for controlling exhaust gases in an oxygen blown converter.
In steel making in a converter using oxygen, as is known, a method has been employed to recover combustible gases, such as carbon monoxide (CO) produced by blast refining, in a state unburnt for re-use as the heat source.
The unburnt gases have been recovered by employment of a method in which the pressure differential between throat pressure i.e. the pressure within the hood, and atmospheric pressure is detected, and an exhaust gas damper is automatically adjusted through an adjusting meter or regulator so that said pressure differential assumes a predetermined value. This method, however, unavoidably poses problems such as so-called blow-out, in which the exhaust gases are emitted out of the throat, and so-called intake phenomenon, in which surplus air is sucked into the throat, due to delay in detection or transmission of signals to rapid variation in quantity of exhaust gases and delay in response of the adjusting meter or the exhaust gas damper produced when the quantity or flow rate of oxygen fed is changed, when secondary material such as iron ore etc. is charged or completed to be charged, or when the quantity or feeding rate of secondary raw material charged is changed in the case where the absolute quantity of the charge is changed. This results in a waste of unburnt exhaust gases and a considerable economical loss due to wasteful burning of the exhaust gases resulting from intake of surplus air.
Thus, in the oxygen blown converter, the method has been employed in an effort to recover the combustible gases, such as CO produced in connection with the blast refining, in a state unburnt, the method normally being called the method for recovering unburnt exhaust gases. For example, see British Pat. No. 1,187,530. A method as controlling means therefore, which is generally called the throat pressure control, is used in which the pressure differential between throat pressure, i.e., the pressure within the hood is detected, and atmospheric pressure. A damper is controlled through a control means so that said internal pressure assumes a predetermined level.
Incidentally, a method is employed to suck surplus air by suitably opening the dust collector damper in order to avoid the surging phenomenon of the draught fan for the exhaust gases despite the fact that the furnace generated gases are in a very small amount at the early stage and at the last stage of blast refining in the converter. This method, however, results in a wasteful burning of unburnt gases, leading to a considerable economical loss.
Further, the aforementioned throat pressure controlling method unavoidably involves delay in detection or transmission of signals and delay in response of control means or damper drive means to repid change in converter reaction thereby inevitably producing phenomenon (blow-out phenomenon), in which the combustible gases are emitted out of the throat, or phenomenon (excessive intake phenomenon), in which surplus air is sucked into the throat, often resulting in an economical loss such as dissipation or wasteful burning of the combustible gases. In addition, the blow-out phenomenon is caused to produce emission of red fume, which is not desirable in terms of environmental health.